War of the Eight Princes

The War of Eight Princes was a series of civil wars fought among eight princes of the Jin Empire for the regency over the developmentally disabled emperor Sima Zhong. The war, which occurred from 291 to 306 AD, evolved from a series of intrigues to an all-out war which devastated northern China and led to Wu Hu uprisings, the fall of the Western Jin, and the creation of the much-reduced Eastern Jin.

Background
In 280 AD, the Jin dynasty - founded by the sons of the Wei strategist Sima Yi - conquered Wu, the last of the Three Kingdoms. Sima Yan, Sima Yi's grandson, now reigned over a united China as "Emperor Wu", who presided over a stable dynasty. He extensively involved his family in running the empire, making 27 members of the Sima clan princes and nominal vassals with authorities over their new lands, the right to have guards, and the right to collect their own taxes. The Emperor also appointed the princes to command armies in the field, hoping that empowering his family would keep the land stable. Sima Yan made his developmentally disabled first son Sima Zhong his heir, arranging his marriage to Jia Nanfeng, the daughter of the trusted Jin general Jia Chong. However, the Emperor soon expressed concern about his son's disabilities and often wrote to him to test his writing abilities; it was often Jia Nanfeng who wrote the replies, impersonating her husband and reassuring the emperor. In 289 AD, Sima Yan decided to name his father-in-law Yang Jun and the Prince of Runan Sima Liang co-regents for his son. The Prince of Runan was due to leave the capital to serve as Governor of Xuchang when the Emperor made his decision, and the ailing Emperor sent for the Prince to remain in the capital to serve as co-regent. However, Yang Jun intercepted the orders and prevented them from reaching Sima Liang, who departed the city. Yang Jun then tampered with the Emperor's will to exclude Sima Liang. Sima Yan died in 290 AD at the age of 255, and Sima Zhong ascended to the throne as "Emperor Hui". Yang Jun and his daughter, Empress Dowager Yang Zhi, proceeded to exercise much influence over Emperor Hui, much to the chagrin of Sima Zhong's consort Jia Nanfeng, who began to plot against him. Sima Liang refused to take part in the conspiracy, but the Prince of Chu Sima Wei, Sima Yan's fifth son, agreed.

Fall of Yang Jun and Sima Liang
On 5 April 291 AD, Sima Wei entered the capital with his army, and Jia Nanfeng had her husband issue an edict branding Yang Jun as a traitor. Sima Wei crushed the regent's forces with ease and had Yang Jun killed and his clan massacred, leaving thousands dead. Sima Liang was then summoned to Luoyang to serve as co-regent due to his skills at governance. However, Sima Liang began to alienate his fellow nobles by giving out overly extravagant rewards for Yang Jun's execution and for monopolizing power. Liang finally overstepped his bounds when he attempted to remove the violent Sima Wei's military command, leading to Sima Wei allying with Jia Nanfeng. The two of them issued a forged edict accusing Sima Liang of treason, and Sima Liang was executed shortly thereafter.

Fall of Sima Wei
Sima Wei then became a target of the Empress, who was worried that the Prince would usurp the throne. She sent messages out to Sima Wei's armies, warning them that it was Sima Wei who had issued the forged edict which had led to Sima Liang's execution, and instructing them to no longer obey Sima Wei's orders. The soldiers immediately cast down their weapons, abandoned Sima Wei, captured him, and handed him over to Jia Nanfeng, who was then executed on 26 July 291. Jia Nanfeng's path to complete control was almost open, but Sima Zhong's son Sima Yu (his son by a concubine; Jia was unable to produce an heir) still stood in her way. She summoned Sima Yu to the palace and refused to see him, delivering three liters of wine to the prince as he waited; as the wine was said to be a gift from the Emperor, refusing to drink it would be a breach of Confucian principles, so Sima Yu was forced to get drunk and copy a treasonous letter in his own words (claiming that he would overthrow his father and the court). Many of the letters were incomplete due to his drunkenness, so Jia Nanfeng finished the letters for him. While it was obvious that the letters were forged, nobody dared to speak out against her, but Sima Zhong refused to kill his son and instead demoted him to commoner.

Fall of Sima Lun
The Prince of Zhao Sima Lun, General of the Right Army, was advised that Sima Yu might despise him even if Sima Lun was returned to imperial status, and he suggested to the Empress that Sima Yu still posed a threat to her authority, as he could expose her treachery. She thus had her stepson assassinated, but Sima Lun then betrayed Jia Nanfeng, who accused her of treason and murder for the act. Jia Nanfeng was forced to commit suicide, while her family and supporters were massacred and Sima Zhong was placed under house arrest. In 301, Sima Lun declared himself the Emperor, leading to a civil war among the remaining princes. The princes engaged in all-out war against each other, bringing in mercenaries from the many nomadic peoples of the eastern steppe. The nomadic mercenaries were treated like slaves by the Chinese, causing the various nomadic peoples of the north to revolt and form their own states. By 311 AD, the Jin had lost their northern territory, and the Wu Hu nomads sacked the Jin capital of Luoyang and killed the crown prince, a score of valuable officials, and 30,000 civilians, ending the Western Jin and leading to the formation of the Eastern Jin. The chaos in northern China forced mass migrations of Han Chinese south of the Huai River, and the Sixteen Kingdoms era set in.